Is there any GUI client that is capable of trading Namecoin, and is somewhat trusted by the community?
A .Net NameCoin GUI was recently posted to Reddit.
I realize that this is a very old question, but I think it makes sense to give an update nevertheless. Recently, a port of the Qt-UI for Bitcoin has been done also for Namecoin. It provides full support also for name operations and even configuring domains directly without the need to come up with the correct JSON strings.